Anti gun groups are going to be protesting and boycotting Starbucks because of their stance on firearms (that they follow state law) and wont ban the possession in their stores. To show support for Starbucks stance and their refusal to cave to the anti gun groups show your support by buying a cup and hanging out for a bit and let them know why you are there that day.
If you plan on being at a starbucks put down the address of the Starbucks you'll be at so others can join you.